This invention relates, in general, to monolithic semiconductor devices and more particularly, to a semiconductor structure having further applicability as a high power, high frequency MESFET power amplifier.
When the prior art was desirous of producing gallium arsenide (GaAs) MESFET devices having high radio frequency (RF) power output, traditionally, the device was made as wide as possible. However, as the width of the device becomes an appreciable fraction of its RF wave-length, both the RF power and the gain per unit width is significantly reduced as its width is increased. This effect becomes more apparent as one endeavors to make very high frequency GaAs MESFET's in the 15 gigahertz (GHz) and higher region of the RF spectrum. As will be hereinafter used, the long dimension of the gate will be referred to as the gate width or periphery while the short dimension refers to the gate length.
One of the prior art difficulties resides in the fact that there is no provision in the conventionally constructed device to permit application of the input signal, in the proper phase, to each part of the device width. Similarly, extraction of the output signal, not in the proper phase over the device width for additive power, contributed to additional power loss.
One method of solving the problem of the dimensional limitations would be to construct the device using transmission line techniques. However, there is no present structure which permits application of a 15 GHz and higher input signal, in the proper phase, to each part of the device width nor is there any structure suitable for the extraction of a properly phased, amplified output signal. Additionally, if the phase velocity of the input signal (at the gate-source transmission line) is significantly different than the corresponding phase velocity of the output signal (at the drain-source transmission line) both the gain of the device and the output power would be significantly reduced.